The objective of this project is to gain insight into the mechanisms underlying the changes in expression of the beta-adrenergic receptors induced by agonists, antagonists, and antidepressant drugs. In the investigation of carbamazepine-induced changes in beta-adrenergic receptor mRNA levels in rat C6 glioma cells, we have focused on the effects of carbamazepine on the homeostasis of calcium and cAMP. There are reasons to believe that mitochondrial function and/or replication are intimately involved in these processes. We have characterized the regulation of intracellular calcium in these calls during stimulation by ATP, serotonin, and isoproterenol. Both ATP and serotonin cause an increase in intracellular free calcium, while isoproterenol does not. Serotonin stimulation causes small changes in beta-adrenergic receptor expression, indicating a cross-regulation between calcium and cAMP generating systems. Glial cells also communicate with one another through gap junctions that permit the influx of calcium. We have found that stimulation of beta-adrenergic receptors causes profound changes in the expression of gap junction proteins, the connexins, that are dependent on call density. We are attempting to obtain a calcium imaging system that will simultaneously monitor calcium and cAMP levels in these cells in order to study the effects of carbamazepine and other drugs on the regulation of these two important second messengers.